Magnetic thin films are deposited for a wide range of applications from magnetic storage to spintronics in order to build smaller and faster nanoscale devices. For example, the magnetic data storage and magneto-electronics industries demand sub-micrometer magnetic structures to operate devices in the gigahertz regime. In addition, as data storage densities grow, industries will require novel magnetic materials that can be patterned rapidly and in a scalable manner.
This disclosure describes how an arbitrary surface may be enhanced with patterned regions of ferromagnetism.
Specifically, a surface may be coated with hydrogenated graphene (HG) and the extent of the magnetism controlled by manipulating the extent of the hydrogen coverage. This can produce films with at least two potential functionalities: ferromagnetic and non-ferromagnetic domains on partially-hydrogenated graphene (pHG). Only partially hydrogenated graphene is ferromagnetic. Both highly HG and graphene are non-magnetic (i.e., diamagnetic).
For 40 years, magnetic hard drive disks (HDDs) enjoyed a growth rate in storage capacity of roughly 50% per year, improving by a factor of 50 million from roughly 2 kbit/in2 in 1956 to around 100 Gbit/in2 in 2006. However, in the past decade, this annual growth rate has slowed from 50% to about 10%. The primary reason for this deceleration is that current HDD technologies are nearing the physical limit of areal density of magnetic domains; that is, magnetic domains of currently used materials cannot be made much smaller than the state-of-the-art 25×250 nm domain size. Thus, the development of new materials capable of supporting precise placement of sub-micrometer magnetic domains is of central importance in advancing modern data storage technology.
Over the last decade, graphene and graphene-based materials have attracted a great deal of attention due to their unique properties, including high mechanical strength, excellent electrical and thermal conductivities, and chemical stability.
Among materials derived from graphene, chemically-modified graphenes (CMGs) show promise for flexible tuning of surface properties. Hydrogenated graphene (HG) is a CMG in which hydrogen atoms are covalently bonded to the basal plane of graphene. The extent of hydrogenation determines the properties of HG and therefore admits a convenient chemical dial for tuning these properties. For example, when graphene is fully hydrogenated, it is a wide-band-gap insulating material. More importantly for the purposes of magnetic storage, partially hydrogenated graphene (pHG) exhibits ferromagnetism, a property which is observed neither in HG nor in pristine graphene.
Here it has been demonstrated that hydrogen atoms can be removed efficiently from graphene by heat, by pressure, or by electron beam to recover its original characteristics. This enables the use of pHG as a host material for patterning a surface with magnetic and non-magnetic regions.
The use of pHG as a patterning host surface has not been realized until now. This invention concerns a method of preparing uniform and stable pHG, combined with an e-beam dehydrogenation (i.e., removal of hydrogen atoms) technique. By using the e-beam to selectively remove hydrogen atoms from certain areas of pHG, arrays of magnetic pHG and non-magnetic graphene patterns are fabricated. Other methods for patterning the hydrogen content can be utilized. Such patterned surfaces can find use in particular in high density data storage application.